In the field of automobile manufacture, substantial efforts are now underway to convert from the use of steel in automotive bodies to aluminum. While welding is a strongly preferred process for joining separately formed sheets to create a unitary automotive body, the well-known difficulties of welding aluminum have heretofore presented serious obstacles to the successful manufacture of aluminum car bodies.
More particularly, in attempting to weld bodies of aluminum, major difficulties have been caused by the fact that aluminum exposed to air immediately begins to form an oxide layer on its surface. Furthermore, the thickness of the layer may vary greatly depending on the time and conditions of such exposure. Thus, in addition to the welding problems caused by the presence of a layer of aluminum oxide, the difficulties have been very substantially increased by the fact that the thickness of the oxide layer may vary greatly from one part to another or even from one area of one part to another area of the same part. These problems make it very difficult to reliably weld even one single point. It has previously been nearly impossible to automate a repetitive process for successive weld points.